Method reference in Java unil BiFunction

Question

I have question about passing method reference as argument in java (util) functions.

I have two functions

Function<Value, Output> f1 = (val) -> {
    Output o = new Output();
    o.setAAA(val);
    return o;
};

Function<Value, Output> f2 = (val) -> {
    Output o = new Output();
    o.setBBB(val);
    return o;
};

I want to merge them into one function which should looked like

BiFunction<MethodRefrence, Value, Output> f3 = (ref, val) -> {
    Output o = new Output();
    Output."use method based on method reference"(val);
    return o;
};

I want to use this function like

f3.apply(Output::AAA, number);

Is it possible ? I can't figure out correct syntax, how to make such a function.

Answer 1

It looks like you want a function like

BiFunction<BiConsumer<Output,Value>, Value, Output> f = (func, val) -> {
    Output o = new Output();
    func.accept(o, val);
    return o;
};

which you can invoke like

f.apply(Output::setAAA, val);
f.apply(Output::setBBB, val);

Answer 2

I'm not quite sure what you mean with "method reference", but I think you want something like this:

BiFunction<Integer, Value, Output> f3 = (ref, val> -> {
    switch(ref) {
        case 1: return f1.apply(value);
        case 2: return f2.apply(value);
        default: throw new IllegalArgumentException("invalid index");
    }
}

You can replace the Integer with anything you'd like, as long as you also change the switch-statement, maybe use an if/else.